Not Applicable
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Not Applicable
The present invention relates to a device for the determination of the degree of relative rotation between two parts or members with respect to each other about a main axis, said device comprising a first detector arrangement, which includes a rotation-imparting element and produces precise information indicating a relative angular position of the two parts within a range of 0xc2x0 and 360xc2x0 C. and comprising a second detector arrangement, which produces information in order to be able to distinguish between full rotations.
Many such devices have been known and are used for the detection of actual values in control and regulating systems, whereby, a first part represents a stationary xe2x80x9cstator,xe2x80x9d in which the second part, the xe2x80x9crotor,xe2x80x9d is supported in a rotatable manner. The rotor may be the rotor of any motor or the shaft of any gear drive or measuring device; and, the stator may be the stator of the motor or a housing or a mount. The preferable, however, not exclusive field of application of the invention herein, is the determination of the relative rotation of the steering wheel of a motor vehicle. In a steering wheel application, the rotor is the steering wheel shaft and the stator is the steering wheel mount or steering column.
Generally, rotation-imparting elements with analog or digital angle sensors are used for the determination of an angle of rotation. Digital angle sensors principally consist of a pattern-bearing arrangement and a pattern-sensing sensor arrangement, which rotate relative with respect to each other corresponding to the relative motion of the two parts. In the case of incremental sensors the pattern-bearing arrangement is a disc or a wheel with marks distributed uniformly over the periphery, the marks being detected by the sensor arrangement and indicated by the generation of corresponding pulses. Successive pulses are counted as a function of the direction of rotation to determine the angle of rotation based on the accumulated sum. In order to use the latter for the determination of the actual position, a reference position must be pre-set and used as reference for the counted value. Usually, this reference position is identified by a separate reference or zero mark, which can be detected by the sensor arrangement. In the case of absolute sensors, however, the pattern is coded as a function of location so that for each angular position an individual sensor signal can be generated, thereby clearly indicating the respective position.
If the range of relative motion is greater than 360xc2x0, i.e., greater than one full rotation, the indication of an angular position produces ambiguous information concerning the actual degree of relative rotation. The same angular positions within successive full rotations cannot be distinguished from each other geometrically. In order to obtain an unambiguous indication, additional measures are required to allow the distinction between full rotations.
An appropriate known measure is a counting of passes as a function of the direction of rotation by means of a reference or zero angle position, as has been disclosed, for example, by literature references DE-C2-3,700,876 and DE-C1-19,508,607 in conjunction with a steering wheel sensor device. These latter known arrangements create particular problems, inasmuch as there is the risk that the counted value is lost when electrical power is shut off or altered due to counting errors; therefore, the entire counter must be initialized periodically in order to calibrate it to zero for a specific reference steering position.
In the known arrangements the selected reference point for initialization is that zero pass, which occurs when the center of the range of relative rotation of the steering wheel is passed and represents the straight-line driving direction. In the arrangement of reference DE-C2-3,700,876, the straight-line driving direction is identified by historical evaluation: a detected zero pass is considered the middle of the range of torsion, unless another zero pass is determined within a predetermined time after the former detection. In the arrangement of DE-C1-19,508,607, the straight-line driving direction is detected by a separate sensor, which recognizes the straight-line position of the steered wheels of the vehicle.
These above-described known devices are complex and susceptible to problems, inasmuch as counting errors, or even counting value losses, occur between initializations; and, therefore, a factor of uncertainty remains.
Reference WO-96/11514 discloses a spiral/pin gear drive. Provided on a stationary disc, concentric to the axis of rotation of the steering wheel, is a spiral groove, in which slides a pin revolving with the steering wheel shaft and which is movable in radial direction. The position of the pin comes into approximate alignment with a mark when the steering wheel reaches the center of its total range of relative rotation. This mark is located either directly on the path of movement of the pin or on the end of a rotary indicator, to which the pin motion is transmitted by means of a lever arm. The ends of the spiral grooves represent the stops for the steering wheel rotation. This known mechanism serves as a positioning aid during assembly of the steering system.
The present invention solves the problem of providing a device for the determination of the degree of relative rotation between two parts or members in such a manner that the device is less prone to trouble; and, the degree of relative rotation between the two parts or members is indicateandreliably, even over more than one full rotation.
In the present invention the second detector device, which provides information permitting the distinction between full rotations, comprises a gear drive driven by the rotation of the two parts with respect to each other and an absolute position sensor for the determination of the position of a measuring element moved by the gear drive. The gear drive has dimensions such that the maximum possible range of the relative rotation of the two parts corresponds to a range of motion of the measuring element, within which all positions can be distinguished from each other by geometric means and which can be resolved by the position sensor at a resolution corresponding to the full rotations between the two parts or members.
The present invention has the advantage that a repeated initialization of the second detector arrangement is not required. When full rotations of the parts occur, the movement of the measuring element remains within a range, the locations of which can be differentiated directly and absolutely. As rotary movements greater than 360xc2x0 occur, an absolute position sensor on the measuring element is capable of making a direct distinction between individual full rotations. The position sensor can be relatively compact and simple, because its resolving capabilities need to correspond only to the number of maximum possible full rotations of the two parts or members.
In one advantageous embodiment of the present invention the gear drive comprises a spiral groove extending concentrically to the main axis on the surface of a disc mounted to a first part and having a number of convolutions corresponding at least to the number of possible full rotations. A pin engages with the spiral groove, the pin being supported on the second part in such a manner that the radial position of the pin changes with respect to the main axis during the movement of the two parts with respect to each other. Mechanical means are used for the connection of the pin with the measuring element.
In the present invention the available absolute position sensor preferably comprises an array of sensor elements mounted to the second part and a sensor object connected with the measuring element. The sensor object moves past the sensor element array when the measuring element is moving, in order to affect, i.e., energize or deenergize, an individual selection of sensor elements in the same manner for each position range, corresponding respectively to a specific full rotation between the parts.
The sensor elements may be light barriers, for example, bifurcated light barriers, whereby the sensor object represents a light-blocking diaphragm array for the selective deenergization of the photoreceivers, or reflected-light barriers, whereby the sensor object is a reflecting array for the selective energization of the photoreceivers. The sensor elements may also be configured as a CCD camera or as specific optical ASICs. Instead of optoelectric sensor elements, it is also possible to use inductive or capacitive elements or elements operating with ultrasound.
The range of motion of the measuring element may be kept relatively narrow because its determination of location may occur with relatively minor resolution. On the other hand some sensor elements such as, for example, light barriers or inductive sensors cannot be configured as small as desired. In one advantageous embodiment of the present invention it is permissible, measured in the direction of movement of the sensor object, for the detection range of the sensor element array and the length of the sensor object to be considerably greater than the maximum deflecting range of the sensor object. In order to permit the absolute determination of location, the sensor object in this case has several partial divisions spaced along its length. These divisions are different from those of the sensor elements such that, for each position range of the sensor object corresponding to a specific full rotation range between the parts, an individual selection of sensor elements is affected in the same sense.
In an alternative embodiment of the present invention, the sensor object may be undivided in its direction of movement and have a length such that it may extend over a number of two or more adjacent sensor elements. This number, preferably, is smaller by 1 (one) than the total number of sensor elements, which, in turn, is preferably smaller by 2 (two) than the number of possible full rotations between the parts. This reduces the risk of ambiguities along the boundaries between respectively two full rotations.
The position sensor can be located directly on the path of movement of the pin sliding in the spiral groove in order to monitor a measuring element placed directly on the pin. In an alternative embodiment, however, the pin movement is transmitted to a measuring shaft by rigidly mounting the pin to the end of an arm, which, in turn, is rigidly connected with the measuring shaft. The latter is rotatably supported in the second of the two parts or members and its axis extends parallel to the main axis; and, the position sensor is designed to determine the position of rotation of the measuring shaft. In this case the sensor object, for example, an aperture array with bifurcated light barriers as sensor elements, preferably is an arcuate element, which is mounted to the measuring shaft and extends in concentric direction to the shaft axis, whereby the sensor elements are arranged appropriately in the manner of a circular arch.
The rotation-imparting element of the first detection arrangement, which indicates the angular position of the two parts or members relative to each other within one full rotation, may be configured in any manner. It may operate with an incremental or any analog or digital absolute angle sensor. In a particular embodiment of the present invention, an angle sensor is used, which comprises a sensor object configured as a pattern disc mounted to the first part or member and having on its periphery a rim with a detectable pattern, and comprises an array of sensor elements mounted to the second part or member for the generation of electrical pulses as the pattern passes. One of the advantages of this embodiment is that the spiral groove can be provided on a surface of the pattern disc. Design advantages may result when the patterned rim projects in the axial direction from the edge of the pattern disc.
The sensor elements of the angle sensor of the first detector arrangement and the sensor elements of the position sensor of the section detector arrangement preferably are located on opposite surfaces of a support disc retained on the second part.
Preferably, the second part is stationary and the first part is rotatable. This applies in particular to the use of the invention for the determination of the relative rotation of the steering wheel of a motor vehicle; in this case the steering wheel shaft constitutes the rotatable of the two parts or members while the support of the steering wheel shaft constitutes the second of the two parts or members.